The aerobic metabolism produces, as side products, reactive
oxygen species (ROS)1 that alter the redox status of cells and tissues.
To maintain suitable concentrations of these species, living organisms
developed antioxidant systems. The first line of defense is the
enzymatic antioxidant system, which neutralizes the action of O2
with superoxide dismutase and of H2O2 with catalase and the glutathione
peroxidase/glutathione reductase system. The second line of
defense is constituted mainly by protein reduced thiols and lowmolecular-weight
antioxidants (LMWAs). The LMWAs comprise a
wide variety of molecules, including dietary products (tocopherols,
ascorbate, retinols, polyphenols, etc.) and metabolic products (urate,
ascorbate, and reduced glutathione), and they are the compounds
that contribute a significant part to the antioxidant capacity of tissues
and biological fluids. Some of these compounds can penetrate
cells and achieve specific locations where the oxidative attack may
be occurring [1–4].